Posted By: gtx6970
MSD 6AL key on voltage connection - 03/21/11 04:26 PM
What is the prefered circuit for the key on signal B+ connection for the MSD box
It's a new M+H Wiring stock underhood wiring harness in a 1970 Road Runner
MSD box is going to be under the battery tray and I plan to use the radiator support for the primary ground and the B+ post on the starter relay for battery positive. And will be routed along the factory fenderwell and firewall wiring but not wrapped into it.
My initial thoughts are the J3 circut off the ignition switch coming thru the firewall bulkhead connector - using the original feed wire for the stock coil ( stock ballast will be there but non-functional)
Posted By: 87MO DAK
Re: MSD 6AL key on voltage connection - 03/21/11 06:40 PM
MSD boxes should power and ground directly off the battery
,and no where else . The trigger wire (small red ) just needs
a 12 volt key on hot wire , to tell the box to switch on.
Posted By: NachoRT74
Re: MSD 6AL key on voltage connection - 03/21/11 07:27 PM
actually with a good power coming from alt and healthy wiring, the B+ source it can be wired from alt post too
the KEY source it can be the blue wire ( brown in 70 and lates ) going from ballast to coil.
Or if thinking on remove ballast resistor, then use the blue wire ( all years ) originally feeding ballast and regulator
Posted By: 87MO DAK
Re: MSD 6AL key on voltage connection - 03/21/11 07:48 PM
Coming directly off the alt will put lots of noise in the MSD box ,
by going directly to the batt the alt noise will get filtered.
Posted By: 70AARcuda
Re: MSD 6AL key on voltage connection - 03/22/11 05:58 AM
just remember the msd start switch will need to see 12 volts both went the key goes to start and went the key is on run...
some 12 volt circuits go to zero volts went the key goes to start...
take the two wires from the ballast resistor...run and start ...and connect both wires to the msd start switch...
Posted By: DirectSubjection
Re: MSD 6AL key on voltage connection - 03/22/11 03:02 PM
I found a 12-volt keyed source under the dash and hooked my MSD to that.
Turns out I hooked it to the key buzzer - my car starts fine but doesn't shut off until I physically remove the key from the ignition slot.
Posted By: gtx6970
Re: MSD 6AL key on voltage connection - 03/22/11 03:49 PM
But if I use the original coil pos connection to supply key start/on voltage signal it's using the ballast resistor .
Running it thru the ballast resistor and I tend to think this is abad idea , correct ?
UNLESS I run a solid wire to bypass it on the backside of the ballast.
It is a MSD dist btw, combined with an MSD blaster 2 coil.
And yes, all the cars body wiring is still stock. One of my goals here is to be able to return it back to stock with minimul effort should the desire to arise sometime in the future.